1. Field of the Invention
This invention relates to a dispenser for fluid substances, in particular creams or liquids, of the type comprising a container defining an elongate chamber to contain the substance and closed at one end by a piston movable along the chamber.
2. Discussion of the Background
A fluid substance dispenser is known provided with a single chamber containing the substance, which is compressed by elastically deforming a portion of the dispenser, in order to deliver it through a discharge nozzle. In these dispensers the piston movable within the chamber is provided with means which prevent it from retracting when the substance is put under pressure.
These means can consist of a toothed rod or the like extending through the entire container chamber from its head and passing through a hole provided in the piston.
At the hole there are provided elements which engage the rod to enable the piston to move only towards the container head.
Each time the dispenser is operated, the rod is lowered within the hole in the piston, which is then dragged by the rod towards the container head when the dispenser ceases operation to return elastically into its rest state (dispensers of this type are described for example in U.S. Pat. No. 2,732,101, U.S. Pat. No. 2,356,874 and U.S. Pat. No. 4,421,255).
In another type of dispenser with a single substance-containing chamber, radially projecting metal lugs are rigid with the piston and have their ends in contact with and pressing against the cylindrical wall of the containing chamber to enable the piston to move only in the direction towards the delivery nozzle. Whenever the dispenser is operated the piston is unable to retract during the compression of the substance, achieved by pressing a deformable part of the dispenser, because of the effect of the lugs.
When said pressing ceases and the first deformed part returns elastically to its rest position, a vacuum is generated in the chamber to cause the piston to rise within the chamber (dispensers of this type are described for example in EP 0051790, EP 0084638, U.S. Pat. No. 3,888,636 and U.S. Pat. No. 3,768,705).
These types of dispensers, comprising a single chamber acting simultaneously as the substance container and the compression chamber for the substance, have the drawback of being very costly (for example because of the provision of the toothed rod and the system for its engagement with the piston, and because of the provision of metal lugs rigid with the piston respectively), of being rather difficult to assemble, and requiring a rather large force for their operation.
To overcome the aforesaid drawbacks dispensers are known having two separate chambers communicating via a non-return valve. Of the two chambers, one is cylindrical and is intended only to contain the substance, it being closed at one end by a sealed piston freely slidable within the chamber.
The other chamber, which acts as the compression chamber, is at least partly deformable (to compress that part of its contained substance which has been drawn through the non-return valve by the vacuum in the collection chamber) and comprises a delivery nozzle provided with a shut-off valve to only allow the substance to pass to the outside.
When delivery ceases, the deformable part returns to its rest position to close the nozzle, and the wall of the cap in returning to its rest position generates a vacuum which draws the substance from the cylindrical chamber to the compression chamber through a non-return valve.
These types of dispenser (described for example in U.S. Pat. No. 4,402,431, EP-A-0097972 and EP-A-0013691) are much simpler than those heretofore described, but have the drawback that the delivery nozzle comprises an elastically closable non-return valve (which opens when the substance is compressed and closes elastically when delivery ceases).
This valve is inserted into a delivery nozzle in which a portion of relatively considerable length lies downstream of said valve.
The result is that if the dispenser is not used for a fairly lengthy period, the substance tends to harden within said nozzle and/or in contact with the discharge valve, to obstruct them or make operation and delivery extremely difficult.
In any event, the sealing of the non-return valve inserted into the nozzle is very problematical because this valve is in direct contact with the substance both upstream and downstream of the valve.